High reactivity, uncooperativeness, and lack of impulse control are characteristics of behavior problems in early childhood. The inability to control or regulate emotions, particularly negative emotions, may be an important antecedent to these disorders. In the present study, we propose to follow a sample of 150 infants, recruited and tested since they were 2 weeks of age, and their parents through the preschool years until 6 moths into their first grade experience, a period when the social contexts of the child expand and study examining the development of emotion regulation and its relation to early behavior problems. This multilevel (infant physiology, infant temperament, parent behavior), multi-informant (mothers and fathers) study has provided a rich database from which continue investigation the developmental pathways toward behavior problems. In the present study we propose to expand our investigation of infant physiology by adding a measure of sympathetic activation (pre-ejection period), observing temperament behaviors, specifically anger reactivity, measuring child behavioral control and regulatory responses, and assessing parent behaviors when subjects are 4.5 and 5.5 yeas of age. Subjects will also participate in a peer interaction before entry into first grade and six months after school entry, teachers and parents will rate problem behavior. Finally, measures of depression, marital satisfaction, life stresses, child rearing disagreements, parent regulatory strategies and family structure will be obtained. By identifying the processes by which children develop problem behavior, preventions and interventions can be more effectively designed and implemented.